On Wed, 2007-01-31 at 10:13 -0500, Mark Lord wrote:
> James Bottomley wrote:
> >
> > For the MD case, this is what REQ_FAILFAST is for.
> I cannot find where SCSI honours that flag. James?
Er, it's in scsi_error.c:scsi_decide_disposition():
maybe_retry:
/* we requeue for retry because the error was retryable, and
* the request was not marked fast fail. Note that above,
* even if the request is marked fast fail, we still requeue
* for queue congestion conditions (QUEUE_FULL or BUSY) */
if ((++scmd->retries) <= scmd->allowed
&& !blk_noretry_request(scmd->request)) {
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
return NEEDS_RETRY;
} else {
/*
* no more retries - report this one back to upper level.
*/
return SUCCESS;
}
> And for that matter, even when I patch SCSI so that it *does* honour it,
> I don't actually see the flag making it into the SCSI layer from above.
>
> And I don't see where/how the block layer takes care when considering
> merge FAILFAST/READA requests with non FAILFAST/READA requests.
> To me, it looks perfectly happy to add non-FAILFAST/READA bios
> to a FAILFAST request, risking data loss if a lower-layer decides
> to honour the FAILFAST/READA flags.
>
> So it's a pretty Good Thing(tm) that SCSI doesn't currently honour it. ;)
James
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